Geoscience Reference
In-Depth Information
Figure 13.3
The oxygen isotope record from ocean core V28-238 modifi ed from
Shackleton and Opdyke (1973). The Brunhes-Matuyama magnetic reversal coincides
with Marine Isotope Stage 19 and this event provided the basis for estimating the age
of the glacial and interglacial stages shown in this core. Shackleton and Opdyke used
a value of 730 ka for this event, but this was later refi ned to 780 ka in the light of
more recent data. Note the rapid transition from cold stages to warm stages - these
are known as Terminations as shown on fi gure 13.5. The global Last Glacial Maximum
corresponds to MIS 2 and the post-glacial or Holocene period corresponds to MIS 1.
term record of continental glaciation it represented) within a robust dating
framework. To achieve this they utilised long-term changes in the Earth's magnetic
fi eld.
Marine isotope stage 19 in core V28-238 coincides with the Bruhnes-Matuyama
magnetic reversal, the last time that the Earth's magnetic fi eld fl ipped. All of the
sediments above MIS 19 have normal polarity. The age of this reversal event was
known and it allowed a timescale to be developed for the entire record based on
the reasonable assumption of a constant rate of sedimentation for deep ocean sedi-
ments. The ages of all sections of the core were interpolated from this datum. This
showed that the Bruhnes Epoch alone contained eight full glacial-interglacial cycles
(fi gure 13.3) and this accounted for much less than half of Quaternary time. In
contrast, the Penck and Brückner model had just four for the entire two million
years or so of the Quaternary Period (table 13.1).
The continuous record of glacial and interglacial cycles from core V28-238 had
a profound impact on Quaternary science and it provided a yardstick against which
all other records could be evaluated. At the end of the decade, Bowen published a
paper in
Progress in Physical Geography
entitled 'Geographical Perspective on the
Quaternary' that drew much of its inspiration from the V28-238 record. It began
with the following statement (Bowen, 1979, p. 167):
A revolution has taken place in Quaternary research that is in effect comparable to
that of plate tectonic theory in the geological sciences as a whole. Its implications
